The culture, 4000A, (Kimball, Corcoran, Wood 1963) was established from a 

 water sample obtained from a depth of 4000 meters at a position 25 miles 

 northeast of Eleuthra. This culture contained 2 species of diatoms, Nitzschia 

 seriata and Navicula sp . 



While none of the cultures including the unialgal were bacteria- free , 

 the experiments were designed to reduce the effects directly attributed to 

 bacteria. L. A. Lanskaja (1961) reported that the bacterial population sharply 

 declined during the phase of active phytoplankLon division and then began to 

 increase when the maximum growth phase for the phytoplankton was reached. With 

 this in mind, all experiments in this study with Sr90-Y-90 and Cs-137 were 

 conducted during the logarithmic growth phase for each culture. However, the 

 exchange portion of the experiments were allowed to progress into the stationary 

 as well as the death phase since it was of interest to learn how much of the 

 radioisotope would be released upon decomposition. 



In growth studies all cultures reached their logarithmic growth phase 

 at two to four days after inoculation. All uptake studies with Sr90 and Y90 

 were carried out during the logarithmic growth phase. The culture was allowed 

 to grow for four days, then additions of zero, one-fourth, on-half, one, two, 

 five, and ten microcuries carrier- free radioisotope were added. The organisms 

 were exposed to the isotope for 48 hours, since most of the organisms in the 

 cultures demonstrated a 48-hour rythmic pattern of cell division. At the same 

 time a flask of each culture was heat killed by autoclaving and ten microcuries 

 of Sr90-Y90 solution added. 



Cell counts were made on the controls and ten ml aliquots were filtered 

 through tared 25-mm (HA) Millipore filter pad. These filter pads were dried, 

 weighed and counted. The dry cell weight was determined and related to the 

 cell count . 



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